1. Field of the Invention
The present invention relates to a pneumatic radial tire. More particularly it relates to an improvement of the bead portion of pneumatic radial tire for a passenger car.
2. Description of the Prior Art
Radial tires have a carcass consisting of a small number of plies, for example, generally one ply or at most two plies, due to the particular carcass structure wherein reinforcing cords are arranged in the radial direction. Therefore, each end portion of the carcass ply is turned up in one direction around a bead wire and terminates in the bead portion. Consequently, the bead portion, in which the turn-up end of the carcass ply is located, is much higher in the stiffness than the side portion due to the difference in the number of plies. Consequently stress is concentrated to the turn-up end of the carcass ply, in which the stiffness changes suddenly, to cause early failures, such as separation and cracks, due to its deformation during the running of the tire.
In order to prevent the above described failures in the bead portion, there has hitherto been proposed a tire structure, wherein a tapered and relatively rigid rubber filler, extends from the upper portion of a bead wire towards the side portion of the tire beyond the above described turn-up end. The filler is arranged between the carcass and the turn-up portion thereof and a rubber chafer is sandwiched between the rubber filler and the lower end portion of a side rubber. As a result, the stiffness is gradually decreased from the bead portion towards the side portion.
However, when tires are exposed to severe running conditions, such as running speed, road surface condition and the like, for a long period of time, the above described structure is still insufficient. The turn-up end has to be additionally reinforced by a cord layer.